Video signals for moving pictures include a luminance signal and two chroma signals Cb and Cr. There are several formats for varying chroma signal resolutions. The 4:2:2 format is typically used for a digital interface in video equipment. An example of this video format includes the SMPTE 292M standard (i.e., HD-SDI) defined by the SMPTE (Society of Motion Picture and Television Engineers) For the purpose of video encoding in consumer products, on the other hand, the 4:2:0 format is typically used.
FIGS. 1A through 1D are drawings illustrating the sample point locations for luminance and chroma signals in the 4:2:2 format and the 4:2:0 format with respect to each of progressive scanning and interlaced scanning as defined in ITU-T H.264. In these figures, the symbol “∘” represents the positions of luminance pixels, and the symbol “Δ” represents the positions of chroma pixels. It should be noted that although the illustration is given such that the horizontal positions of chroma pixels are slightly displaced from the positions of the luminance pixels for the sake of clarity, these pixels actually occupy the same horizontal pixel positions. As illustrated in FIG. 1A, the chroma samples are decimated by a ratio of 2:1 relative to the luminance samples in the horizontal direction for the progressive 4:2:2 format. In the vertical direction, however, the number of chroma samples is equal to the number of luminance samples. In the progressive 4:2:0 format illustrated in FIG. 1B, on the other hand, the number of chroma samples is decimated by a ratio of 2:1 relative to the number of luminance samples in both the horizontal direction and the vertical direction.
FIG. 1C illustrates the interlaced 4:2:2 format. The interlaced video frame is comprised of a top field and a bottom field. For both luminance and chroma components, the top field is formed by the even-numbered lines (i.e., 0, 2, 4, 6, . . . , lines starting from 0) taken out from the progressive 4:2:2 format frame illustrated in FIG. 1A. For both luminance and chroma components, the bottom field is formed by the odd-numbered lines (i.e., 1, 3, 5, 7, . . . , lines) taken out from the progressive 4:2:2 format frame illustrated in FIG. 1A.
FIG. 1D illustrates the interlaced 4:2:0 format. For both luminance and chroma components, the top field is formed by the even-numbered lines (i.e., 0, 2, 4, 6, . . . , lines starting from 0) taken out from the progressive 4:2:0 format frame illustrated in FIG. 1B. For both luminance and chroma components, the bottom field is formed by the odd-numbered lines (i.e., 1, 3, 5, 7, . . . , lines) taken out from the progressive 4:2:0 format frame illustrated in FIG. 1B. As can be seen by comparing FIG. 1C and FIG. 1D, the number of chroma pixels in the interlaced 4:2:0 format are decimated by half in the vertical direction relative to the chroma pixels in the interlaced 4:2:2 format. In various standards for moving picture encoding such as MPEG-2 and H.264/MPEG-4 AVC, the 4:2:0 format is widely used. MPEG-2 and H.264/MPEG-4 AVC support the 4:2:2 format in addition to the 4:2:0 format. While consumer products typically employ the 4:2:0 format, equipment that employs the 4:2:2 format may typically be limited for professional use.    [Patent Document 1] Japanese Patent Application Publication No. 2000-92512    [Patent Document 2] Japanese Patent No. 3292486    [Non-Patent Document 1] “Problem and Solution of Current TV/HDTV Compatible Encoding Scheme,” The Institute of Electronics, Information and Communication Engineers, Proceedings of Spring Conference, D-334, 1992